This invention relates to a cylinder head for an internal-combustion engine of the type having a plurality of charge cycle valves, arranged at respective sides of a longitudinal center plane of the cylinder head.
U.S. Pat. No. 4,637,356 discloses a valve gear comprising three intake valves actuated by a camshaft, the center valve of these intake valves being actuated in line by means of a rocker lever and the two exterior valves being actuated directly by way of bucket tappets.
From German Patent Document DE-36 00 408 C2, a cylinder head is known which has three intake valves and in the case of which a separate intake pipe provided with a throttle valve and an injection valve is assigned to each intake port. For generating a swirl movement of the charge, only a single exterior intake valve is actuated in a first operating range. As the rotational speed increases, the throttle valves and injection valves of the second and third intake valve are actuated successively.
It is an object of the invention to provide a cylinder head for an internal-combustion engine with improved power and torque values.
This object is achieved by means of a cylinder head for an internal-combustion engine comprising a first group of charge cycle valves arranged on one side of a cylinder head longitudinal center plane, said first group of charge cycle valves being spaced from one another along a circumferential direction about a central axis of an engine cylinder when the cylinder head is in an operative position on an engine, a first camshaft for actuating the first group of charge valves, and an operating lever operatively connected to the first camshaft for continuously acting on one charge valve of the first group, said remaining charge valves of the first group being selectively actuated by the first camshaft.
If, in the case of a cylinder head of the above-mentioned type, a charge cycle valve, which is first in the circumferential direction of each cylinder and is arranged in line with an actuating lever, is actuated permanently and the other valves of this group are actuated at times, this cylinder head is optimized with respect to the charge cycle and furnishes an increased power and torque yield.
Because of the absence of a space-consuming bucket tappet, the permanently operated valve permits a space-saving arrangement at the edge of a combustion chamber. The resulting tangential inflow causes a targeted rotating charge movement ("swirl"). The radial arrangement of this valve makes it possible to design the valve or the additional valves of the first group to be comparatively large and to therefore achieve an optimal mixture flow rate for high performances. Since this increased mixture flow rate is required only at high loads, the additional valves can be connected or disconnected by means of switching mechanisms.
These mechanisms may be designed in multiple manners; thus, for example, as a switching arrangement according to German Patent Document DE-40 27 630 C integrated into a hydraulic tappet or as devices according to German Patent Document DE-41 00 763 A which couple and uncouple the corresponding cams to and from the camshaft, and are therefore not discussed in detail.
For a further optimization, a first separate intake pipe is assigned to the permanently operated charge cycle valve which is constructed as an intake valve, and another intake pipe is assigned to the additional valves of this group. With respect to their geometry, the intake pipes can therefore be adapted to the different requirements of a low-load or a high-load operation.
If the cylinder head is operated on a spark-ignited internal-combustion engine, corresponding arrangements for the supply of fuel are assigned to these intake pipes, and a shaft which is arranged centrally in the cylinder head above each cylinder is used for receiving the spark plug.
On a spontaneous-ignition internal-combustion engine, this shaft instead houses the arrangement for the supply of fuel.
If the first group of charge cycle valves has, for example, three intake valves, the internal-combustion engine can be operated in a fuel-saving manner at low loads by means of only one first intake valve which has a comparatively small diameter. An exhaust valve of the second group may be equipped with a switching mechanism in the same manner. The internal-combustion engine may then be operated as a two-valve engine, in which case only a low driving power is required for the valve gear.
In the case of increasing loads, the two additional intake valves and the second exhaust valve will then be connected isochronously or successively. The mixture flow will then take place essentially by way of the additional valves which are dimensioned to be comparatively large so that the internal-combustion engine may then be considered to be a power-optimized 4-valve engine.
In a further advantageous development, the angular positions of the longitudinal center axes of the charge cycle valves are selected such that a combustion chamber roof is obtained which is as smooth as possible and has no fissures. As a result, a knocking combustion is largely avoided, and the knock limit is displaced in the direction of a higher power yield.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.